One such device of a known type is a chip-type micro-reactor. A chip-type micro-reactor has a plurality of interconnected channels connecting a plurality of reservoirs for holding liquids. Liquids from the reservoirs are moved into and through the channels where they mix in a controlled manner. Controlled mixing is often used to control chemical reactions, e.g. between solutes in the liquids. One way in which the liquids can be moved is by generating an electro-osmotic force in the channels, the electro-osmotic force driving the liquids through the channels. Electro-osmotic force is a well known type of electrokinetic force and is described in detail in “Development and operating characteristics of micro flow injection analysis systems based on electro-osmotic flow”, by S. J. Haswell, Analyst, 1997, Vol. 122, 1R–10R (the contents of which are incorporated herein by reference). Another electrokinetic force is electrophoresis.
A problem, however, with such micro-reactors is that differences in liquid levels in the reservoirs lead to hydrostatic forces acting on the liquids, tending to move the liquids through the channels. It is often desirable to minimize liquid flow caused by hydrostatic fore.
According to the invention, there is provided a device having a flowpath therein for electrokinetically driven liquid flow therealong, the device comprising at least first and second members together having a first groove with a larger cross-sectional area and a second groove with a smaller cross-sectional area, the members together having at least one surface and being connected together so that the at least one surface closes the first and second grooves to form respective first and second channels in said flowpath with larger and smaller cross-sectional areas respectively, the cross-sectional area of the second channel being such that the second channel resists hydrostatically driven liquid flow along the flowpath.